Rare Earth Magnets are including Neodymium(Nd)-Iron(Fe)-Boron(B) types and Samarium(Sm)- Cobalt(Co) classes. The most commonly produced material is neodymium-iron-boron (NdFeB), a type of rare earth alloy that typically has two atoms of Neodymium (Nd), 14 atoms of Iron (Fe), and one atom of Boron (B) as its primary elements, hence their chemical composition Nd2Fe14B, which is commonly abbreviated as NdFeB.
NdFeB magnets are very powerful. They have a higher Maximum Energy Product, (BH)max, than SmCo magnets. (BH)max of NdFeB can easily reach 30 MGOe and even goes up to 52 MGOe. NdFeB magnets can replace SmCo magnets in most cases, especially where operating temperature is less than 80°C.
The temperature stability of NdFeB is not as good as SmCo magnets. Magnetic performance of NdFeB magnets will deteriorate rapidly above 200°C. Compared to SmCo magnets, the corrosion and oxidation resistance of NdFeB is relatively low. Therefore, A surface coating is usually applied on NdFeB magnets. Zinc or nickel coating is common used as a protective layer. Other materials such as gold, brass, tin or polymer (epoxy) are also used for this purpose.